The present invention relates to a catheter adapted to be inserted into a blood vessel in order to perform various analyses in the body of a living being, such as in the heart, the liver, the kidney, a pulmonary artery, or, a limb.
Microdialysis is used to monitor the interstitial fluid in various body organs with respect to local metabolic changes. The technique is also experimentally applied in humans for measurements in adipose tissue.
U.S. Pat. No. 4,694,832 discloses a dialysis probe comprising a dialysis membrane with associated ducts for achieving a perfusion fluid flow over the membrane. The single membrane is tubular and consists of a thin-walled permeable hose material referred to as a xe2x80x9chollow fiberxe2x80x9d membrane. Ducts are provided for supplying and removing perfusion liquid to and from the interior of the membrane, and one of these ducts is disposed inside the hollow fiber membrane to extend to the distal end thereof. In order to protect and support the very thin membrane, the membrane is surrounded by a mounting, which is more rigid than the membrane and is preferably made as a thin-walled metal sleeve. The membrane is inserted in the mounting to be as close as possible to the wall of the sleeve. The wall of the sleeve has an opening in which a portion of the membrane surface is exposed. Although the size of this opening may vary depending on the desired size of the dialyzing surface of the membrane, it is evident that it cannot be large enough to meet all requirements for optimum dialysis, since then the protective and support properties of the sleeve would be lost.
U.S. Pat. No. 5,106,365 discloses a microdialysis probe comprising an outer sleeve containing tubes for delivering and removing dialysis products. The dialysis membrane is directly fixed to the end edge of the outer sleeve by gluing. This prior art probe is not suited for insertion in a blood vessel since the membrane constitutes the tip of the probe.
U.S. Pat. No. 5,441,481 discloses a microdialysis probe arranged to have a primary probe, e.g., an electrical probe, concentrically located within it to enable the combined microdialysis probe and primary probe to be extended as a unit through a common opening into the body of a living being. The microdialysis probe comprises a tube having a lumen therethrough for releasably mounting the primary probe, and at least one dialysis chamber. The dialysis chamber comprises a wall formed of a semi-permeable material, an inlet passageway to the chamber and an outlet passageway from the chamber.
Reference is made also to SE 9800791-7 (filing date Mar. 11, 1998) and PCT/SE99/00259 (claiming priority from SE 9800791-7 and having a filing date Feb. 24, 1999), both by the same inventors and neither published at the filing date of the present application. The prior application concerns a catheter to be inserted into and guided by a blood vessel, and it comprises an elongate catheter body, having a distal end and a proximal end. An outer essentially cylindrical surface, limiting a wall structure, encloses at least two channels including a first and a second channel for microdialysis solution, each channel having a proximal end and a distal end. The first and second channels are interconnected at a first distance from the distal end of the catheter body so that microdialysis solution can flow from one channel to the other. An opening is provided in the catheter body at a second distance from its distal end, and a microdialysis membrane is arranged in to cover the opening. A space in the catheter body formed by a portion of the first channel in connection with the opening forms a microdialysis chamber, having at least a portion of the microdialysis membrane as a part of its walls. The proximal ends of the first and second channels are connectable to external means for circulating, monitoring and/or analyzing the dialysis solution.
Although this prior microdialysis catheter represents a major step forward in the art of microdialysis, it still suffers from the main drawback of all prior art microdialysis catheters, viz. a low ratio of area to volume, i.e. the effective area of the membrane in relation to the volume of dialysis solution passing the membrane per unit of time. In order to obtain the best possible recovery, it is important that the relationships of area to volume is as high as possible.
It is an object of the present invention to provide a new catheter intended for insertion into a blood vessel for performing blood analysis, primarily by microdialysis, said catheter being provided with membrane means enabling a maximum effective area of microdialysis membrane and a minimum of volume flow of perfusion fluid (perfusate).
To achieve this object, the present invention proposes, instead of the conventional use of a continuous sheet of membrane, or, as in U.S. Pat. No. 4,694,832, the use of one single tubular membrane, the use of a plurality of tubular membranes the interiors of which together constitute the dialysis chamber. Thus, one end of each such tubular membrane is connected to a common delivery channel for perfusion fluid and the other end of each such tubular membrane is connected to a common discharge channel for perfusion fluid, thus achieving parallel flows of perfusion fluid through the membranes, whereas the exteriors of all the tubular membranes are caused to contact the blood to be analyzed. It is preferred to arrange all tubular membranes along the periphery of a cylinder, either parallel to the cylinder axis or in a helical manner.